KL-6 may be a useful biomarker in patients with interstitial lung disease, but there is limited information in non-Asian populations. Therefore, it is necessary to carry out studies in other populations to confirm the diagnostic values of the biomarker and its prognostic implication.

Hypothesis KL-6 may be a useful biomarker in the management of interstitial lung diseases. But it is necessary to know more about its utility in the European population.

Study Objectives:

• To determine the concentration of KL-6 in serum of patients with pulmonary fibrosis at the time of diagnosis compared to patients without pulmonary fibrosis
• Diagnostic yield of KL-6 in patients with pulmonary fibrosis.
• Correlation of KL-6 values with functional and radiological parameters of disease severity at diagnosis.
• Correlation of serum KL-6 values with the evolution of the disease.

Inclusion Criteria:

1. Subjects older than 18 years.
2. Chronic respiratory diseases )including Fibrotic interstitial lung disease, asthma or COPD) related or not to a connective tissue disease.
3. Acceptance of the patient to participate in the study by signing the informed consent after having discussed with the researchers the objectives, risks and potential benefits.

Exclusion Criteria:

1. Absence of informed consent
2. Psychiatric disorder or limitation of collaboration (including language, socio-cultural problem, etc.).

Subjects over 18 years of age attending the outpatient clinic at Hospital de la Santa Creu i Sant Pau.